It is well known to administer drugs to or through the skin or mucosa. Such a mode of delivery provides many advantages; primarily, topical, transdermal or transmucosal delivery are generally comfortable, convenient and noninvasive ways of administering drugs. The variable rates of absorption and metabolism encountered with oral treatment are avoided, and other inconveniences--gastrointestinal irritation and the like--are eliminated as well.
A number of problems have been encountered with the aforementioned modes of drug administration, however. The skin or mucosa can become irritated or sensitized by a particular drug, adhesive or skin permeation enhancer. Pain and itching may result and be serious enough that the patient may discontinue use of the drug. In addition, the skin may become dry or flaky upon continued administration of a particular pharmaceutical composition. If such problems persist and are severe enough in a large fraction of patients, a particular drug may simply be designated as unsuitable for administration to the skin or mucosa, even though therapeutically effective blood levels may have been achieved by administering the drug in this way.
The present invention is premised on the completely unexpected discovery that the oil extracted from the Yerba Santa plant (Eriodictyon californicum; Eriodictyon glutinosum; also known as "eriodictyon fluid extract"; "consumptive's weed"; "bear's weed"; "mountain balm"; and "gum plant") is extremely effective as an excipient in compositions for application to the skin or mucosa, and minimizes or completely eliminates the irritation, sensitization and dryness which often accompanies topical, transdermal or transmucosal drug delivery. The novel excipient also makes possible the administration of a wider range of drugs than previously believed possible, i.e., drugs which caused a significant degree of the aforementioned problems in a relatively large fraction of patients.
The Yerba Santa plant is an evergreen shrub indigenous to the hills and mountains of California and northern Mexico, and was long used by Indians for a number of purposes. See, e.g., A. R. Hutchens, Indian Herbalogy of North America, Ontario: Merco, 1975, at pp. 317-318. A number of references to the Yerba Santa plant teach its use as an expectorant (e.g., N. Coon, The Dictionary of Useful Plants, Emmaus, Pa.: Rodale Press, 1974)), in treating colds, sore throats, catarrh, stomach aches, vomiting and diarrhea (see A. R. Hutchens, supra), in treating hemorrhoids (D. G. Spoerke, Herbal Medications, Santa Barbara, Calif.: Woodbridge Press, 1980, at p. 183), in treating diseases of the lung (Los Remedios de la Gente: A Compilation of Traditional New Mexican Herbal Medicines and Their Use, compiled by M. Moore, 1977), and in masking the taste of quinine and other bitter medications (Spoerke, supra; see also G. E. Trease et al., Pharmacognosy, London: Cassell & Colber, 1978, at p. 463)). However, the present discovery that eriodictyon fluid extract is extremely effective in ameliorating the problems associated with delivery of certain drugs to the skin or mucosa is believed to be novel and completely unsuggested by the art.